South Africa’s long history with floating invasive macrophytes has led to a large body of research into this field, whereas submerged invasive macrophyte studies are far fewer. This study aims to understand the driving mechanisms underlying Egeria densa Planch (Hydrocharitaceae) invasions in South Africa, by investigating the ability of this species as a resource competitor against submerged native species, helping to predict where it is likely to establish and to what degree of success. This will enable informed management decisions, including the importation and potential release of the leaf mining fly Hydrellia sp. nv.; a promising biological control agent. To further understand the mechanisms of submerged macrophyte invasions, this study will explore the role of alternate stable states. If shifts from invasive floating stable states can result in invasive submerged stable states, the rapid control of floating plants could be the catalyst promoting the invasion of E. densa in South Africa. This would provide an opportunity for systems to be purposefully managed to induce shifts promoting native submerged stable states. Furthermore this project aims to use the application of stable isotope tracing to measure the functional response of E. densa in intraspecific and interspecific contexts. This project aims to investigate the ecology of E. densa with the end goal of improving predictions of establishment and success, leading to more efficient management.